According to EP 1 420 158 A2 (JP-A-2004-162665), an exhaust gas recirculation apparatus (EGR apparatus) is disclosed as an example of a fluid control valve. An internal combustion engine discharges exhaust gas from a combustion chamber thereof, and the EGR apparatus recirculates the exhaust gas as EGR gas partially into an air intake system of the engine. An exhaust gas recirculation valve (EGR valve) is provided midway through an exhaust gas recirculation pipe (EGR pipe) of the exhaust gas recirculation apparatus (EGR apparatus).
As shown in FIG. 6, the EGR valve 200 is constructed of a housing 101, a butterfly valve 102, a valve shaft 103, a coil spring 104, and a valve actuator device. The housing 101 is formed by die-casting of an aluminum material such as aluminum alloy. The butterfly valve 102 is movable in the housing 101. The valve shaft 103 is rotatable together with the butterfly valve 102. The coil spring 104 biases the butterfly valve 102 such that the butterfly valve 102 blocks a fluid passage in the housing 101. The valve actuator device actuates the butterfly valve 102.
The EGR valve 200 further includes a seal ring 105 provided to the outer circumferential periphery of the butterfly valve 102. The butterfly valve 102 is fixed to the tip end of the axis of the valve shaft 103 in a condition where the butterfly valve 102 is inclined with respect to the axis of the valve shaft 103 by a predetermined angle. The valve actuator device is constructed of an electric motor and a transmission device such as reduction gears. The electric motor generates driving force by being supplied with electricity. The transmission device transmits the driving force of the electric motor to the valve shaft 103. The housing 101 includes a cylindrical portion (gas passage portion) 107 and a valve bearing portion 108. The cylindrical portion 107 defines therein an exhaust gas recirculation passage (EGR passage) 106 being substantially circular in cross section. The valve bearing portion 108 rotatably supports the valve shaft 103.
A cylindrical nozzle 109 formed of a stainless steel is press-inserted into the fluid passage of the housing 101. The cylindrical nozzle 109 is arranged in a sliding portion in the vicinity of the full close position of the butterfly valve 102. The seal ring 105 has the seal ring sliding surface 66, which slides on the sliding portion of the cylindrical nozzle 109. The housing 101 has a cooling water passage 110 through which cooling water is circulated. In this structure, when exhaust gas, which is less than 400° C. in temperature, passes through the EGR passage 106, the housing 101 can be maintained lower than allowable temperature limit thereof.
In an engine of a vehicle such as an automobile, high-temperature exhaust gas, which is higher than 500° C. in temperature, may pass through the EGR passage 106. In this case, even cooling water is supplied through the cooling water passage 110, temperature of a housing 5 becomes greater than the allowable temperature limit due to thermal transmission from high-temperature exhaust gas.
When temperature of the housing 5 becomes greater than the allowable temperature limit, the gas passage portion 107 of the housing 101 may be deformed, consequently, circularity of the EGR passage 106 may decrease. In addition, as a cast defect such as a defect hole, a blowhole, a pinhole, and shrinkage becomes large, the surface of the housing 101 may swell As a result, the appearance of the housing 101 may be degraded, and consequently, quality such as rigidity and durability of the housing 101 may be also degraded.
When the engine discharges high-temperature exhaust gas higher than 500° C. in temperature, heat quantity transmitted from the housing 101 to components in the housing 101 increases. As a result, temperature of the components in the housing 101 also becomes higher than the allowable temperature limit thereof.
In particular, an oil seal 111 such as a seal rubber may be provided to the valve bearing portion 108 for restricting lubricant from leaking into the butterfly valve 102. In this structure, the oil seal 111 may be deteriorated due to heat transmitted from the high-temperature exhaust gas. Alternatively, the metallic bush 112 may be substituted to a sintered oil bearing, and the sintered oil bearing may be provided in the valve bearing portion 108. In this structure, oil may weep out of the sintered oil bearing due to heat transmitted from the high-temperature exhaust gas. Consequently, lubrication of the valve bearing portion 108 may be deteriorated.
The material of the housing may be changed from aluminum die cast to cast iron to enhance heat resistance of the housing 101. However, cast iron is less than aluminum die cast in dimensional accuracy. Accordingly, when the material of the housing 101 is changed from aluminum die cast to case iron, a cast-iron product of the housing 101 needs to be applied with machining works for accurately manufacturing the inner and outer peripheries thereof so as to obtain predetermined dimensional accuracy. As a result, manufacturing cost may drastically increase.